Conventionally, a hierarchical database (for example, one disclosed in the Information Processing Handbook, page 902) has been adopted as a main database provided in an information processing system, and diverse attempts have also been made to allow an access from a World Wide Web (Web) system to the hierarchical database. For example, there is a method of enabling a Web system to link up with a legacy system by converting a hierarchical database to a relational database, or a method of enabling a Web system to link up with a legacy system by preparing a bridge program for calling or invoking a hierarchical database between the Web system and the legacy system.
The former method of converting the hierarchical database to the relational database is efficient for migrating the legacy system into an open environment. However, conversion of the main data updated daily requires sufficient care for timing of conversion and/or for preservation of consistency of the data. Moreover, in this method, identical data needs to be held in different data formats, resulting in necessity of extra storage capacity for the data to be stored in both formats.
The latter method of employing the intervention of the bridge program for invoking the hierarchical database requires creating the bridge program for enabling it to access the hierarchical database. As a result, a change in the program of the hierarchical database leads to a need to change or update the bridge program. Moreover, any provision of an unconventional access method from the Web system will also lead to the need to change or update the bridge program to respond thereto.
There is also known an access method from the Web system to data constituted by XML data as described in the article “XML Data Management by Object Database,” by Iwaki et al. In this description, a database to be accessed is not a hierarchical database, so that an existing hierarchical database might not be used as a main database in this method.